Marcel Filoche Seminar: Modeling and Designing Micro-Optoelectronic Devices in the Real World: The Role of Disorder

April 15, 2014 | 4:00pm | ESB 1001

Faculty host: Jim Speck

>>>Video and slides available after the presentation*

Abstract

In
the last decade, the constant reduction in size and the growing
number of material interfaces in electronic or optoelectronic
devices (such as MQW-LEDs, organic or inorganic solar cells, ...)
has boosted the impact of the intrinsic disorder present at smaller
scales of materials. This disorder can originate from compositional
inhomogeneities, from interface roughness or from lattice defects.
Any realistic modeling should therefore account for these
imperfections relative to the perfect homogeneous material as they
can drastically impact the carrier transport or the coupling between
carriers and light at the submicron level. Yet, to this day, very
few or almost no simulation tool faithfully accounts for the effects
of this disorder in the design of structures and devices.

We will present a paradigmatic case of such disorder-induced
alteration, called "wave localization", and show how the issue of
modeling disorder in quantum devices can be addressed in a efficient
and systematic way.

In a disordered or random solid,
electronic states can display a fascinating property i.e., the
strong localization of their wavefunctions. Unlike the Bloch waves
which are delocalized in the entire system, these wavefunctions are
concentrated in a very limited region despite the absence of any
apparent confining potential. Discovered in 1958 by Anderson (1977
Nobel Prize for this discovery), the mechanism of the
disorder-induced localization still remains to this day mysterious
for a large part. In particular, until recently it seemed very
difficult or even impossible to predict the location of the
localized states in a specific sample. Modeling carrier transport in
a heterogeneous medium therefore usually requires recomputing all
relevant eigenfunctions and eigenvalues of the corresponding
Hamiltonian, a very tedious and time-consuming task, impossible to
carry out in a full sized device.

In this seminar, we will
present a totally new geometrical approach to localization. This
theory is not restricted to quantum states, and can be applied in
fact universally to all physical waves. It exhibits in any system a
partition of disjoint regions which host the localized states, these
regions acting as weakly coupled oscillators. The theory not only
predicts localization of states at lower energies, but also the
transition towards delocalized states at higher energy. Most of all,
it allows for the first time to directly derive, by solving only
one simple Dirichlet mathematical problem, yielding a function
called "landscape" that determines the boundaries of the regions
where one can expect the presence of localized states, and the
energies of the transition to delocalised states .

We
will show how computing this "landscape of localization" provides
all the relevant information about localization, density of states,
or average spatial distribution. Finally, we will propose a scheme
to implement this new approach towards understanding and controlling
the materials properties of heterogeneous or disordered systems or
devices.

Biography

Marcel
FILOCHE (P.I.) is Directeur de recherche CNRS, deputy director
of the laboratory "Physique de la Matière Condensée" at Ecole
polytechnique, and Professor at the École des Mines de Paris. He
graduated from Ecole Polytechnique and got a PhD from the Université
d'Orsay in semiconductor physics. His main research topic deals with
the properties of systems of complex geometry. He is author or
co-author of about 80 publications in peer reviewed journals.

*video and slides only available for seminars if approved.

An Energy Frontier Research Center of the Department of Energy Office of Basic Energy Sciences